Wrong. I guess you are a newbie in the sports-betting area. The house makes money from sports-betting through margin or juice which varies based on the sport, market type etc.
Some sports-betting sites charge high margins(Stake etc) while some charge low margins(Pinnacle etc). Betting exchanges charge zero or negligible margin since they earn through commissions on the bets.
To be honest, I have never reviewed such charges, is that when I do sports bets, I usually do not sit still and start playing poker and blackjack, and since I saw that there were no relevant amounts that I was losing, I did not review the clear gallery it is logical somehow the house must win by placing those services.
They earn with sports betting and take profit margin from the bets from side a or side b. It just so happens that you cannot notice it because your whole amount bet is still there and won't change once you bet and it's only increasing when you've won already. And when there's already a winner, that's when they're going to take their profit margin and will be distributed to the bettors who have won those bets while taking a chunk from those bettors who have lost and that's why they've got some percentage and those odds that we see from stake and other sports book are different.